Hi there @Parn,
you can try following approach as well. Split your table on two tables. One with 2017-2018 data and another with 2019 data. Then feed 2017-2018 data into Counting Loop Start node which will have go 12 iterations (under assumption you have full 2019 data). In each iteration you can filter your 2019 data based on currentIteration flow variable (+1 cause it starts from 0) to have only January in first iteration, Jan and Feb in second and so on.
Something like this:
Drop me a message if you need example. Hope this helps!
Br,
Ivan